The invention relates to the field of intraluminal catheters, and particularly to guiding catheters suitable for intravascular procedures such as angioplasty, stent deployment, pacing lead deployment and the like.
In percutaneous transluminal coronary angioplasty (PTCA) procedures a guiding catheter having a shaped distal section is percutaneously introduced into the patient""s vasculature and then advanced through the patient""s vasculature until the shaped distal section of the guiding catheter is adjacent to the ostium of a desired coronary artery. The proximal end of the guiding catheter, which extends out of the patient, is torqued to rotate the shaped distal section and, as the distal section rotates, it is guided into the desired coronary ostium. The distal section of the guiding catheter is shaped so as to engage a surface of the ascending aorta and thereby seat the distal end of the guiding catheter in the desired coronary ostium and to hold the catheter in that position during the procedures when other intravascular devices such as guidewires and balloon catheters are being advanced through the inner lumen of the guiding catheter.
In the typical PTCA or stent delivery procedures, the balloon catheter with a guidewire disposed within an inner lumen of the balloon catheter is advanced within the inner lumen of the guiding catheter which has been appropriately positioned with its distal tip seated within the desired coronary ostium. The guidewire is first advanced out of the distal end of the guiding catheter into the patient""s coronary artery until the distal end of the guidewire crosses a lesion to be dilated or an arterial location where a stent is to be deployed. A balloon catheter is advanced into the patient""s coronary anatomy over the previously introduced guidewire until the balloon on the distal portion of the balloon catheter is properly positioned across the lesion. Once properly positioned, the balloon is inflated with inflation fluid one or more times to a predetermined size so that in the case of the PTCA procedure, the stenosis is compressed against the arterial wall and the lumen dilated to open up the vascular passageway. In the case of stent deployment, the balloon is inflated to plastically expand the stent within the stenotic region where it remains in the expanded condition. Generally, the inflated diameter of the balloon is approximately the same diameter as the native diameter of the body lumen being dilated so as to complete the dilatation or stent deployment but not overexpand the artery wall. After the balloon is finally deflated, blood flow resumes through the dilated artery and the dilatation catheter and the guidewire can be removed therefrom.
Generally, the stent deployment may be accomplished simultaneously with or after a PTCA procedure has been performed at the stenotic site.
In addition to their use in PTCA and stent delivery procedures, guiding catheters are used to advance a variety of electrophysiology-type catheters and other therapeutic and diagnostic devices into the coronary arteries, the coronary sinus, the heart chambers, neurological and other intracorporeal locations for sensing, pacing, ablation and other procedures. For example, one particularly attractive procedure for treating patients with congestive heart failure (CHF) involves introduction of a pacing lead into the patient""s coronary sinus and advancing the lead through the patient""s great coronary vein and a branch of the great coronary vein until the distal end of the pacing lead is disposed at a location which allows the electrical impulse from the pacing lead to pace the left ventricle of the patient""s heart. A second pacing lead may be disposed within the patient""s right ventricle or a cardiac vein draining the patient""s right ventricle and both the left and right ventricle may then be paced by the pacing leads, resulting in greater pumping efficiencies and greater blood flow out of the heart which minimizes the effects of CHF.
Current construction of many commercially available guiding catheters include an elongated shaft of a polymeric tubular member with reinforcing strands (usually made of metal, high strength polymers or combinations thereof) within the wall of the tubular member. The strands are usually braided or wound into a reinforcing structure.
Clinical requirements for utilizing guiding catheters to advance catheters and other intravascular devices have resulted in a need for increased transverse dimensions of the inner lumens of guiding catheters to accommodate a greater variety of larger intracorporeal devices and for decreased outer transverse dimensions of the guiding catheter to present a lower profile which facilitates further advancement within the patient""s body lumens and openings. These catheter design changes have required a reduction in the wall thickness which in turn requires a reduction in the ratio of polymer to stranded reinforcement and a reduction in the strand thickness. This all results in a catheter shaft which is not very visible fluoroscopically due to the low level of radiopacity.
What has been needed is a catheter design which would allow for continued thinning of the catheter wall for increased lumen size and lower outer profiles, while providing the strength and radiopacity levels that are clinically desirable for such products. The present invention satisfies these and other needs.
The invention is generally directed to a thin walled intraluminal catheter such as a guiding catheter with a multistrand reinforcing structure which has improved radiopacity with little or no reduction in structural properties of the catheter wall.
The guiding catheter of the invention has an elongated shaft with a preshaped distal shaft section to facilitate placement of the distal tip of the catheter. The shaft has a multistrand reinforcement, preferably within the wall of the shaft, which may be braided or wound. At least one of the strands of the reinforcing structure is formed of an alloy having at least 50% by weight, preferably at least 65% by weight of one or more suitable refractory metals. Suitable refractory metals include molybdenum, tungsten, rhenium, tantalum and niobium.
The radiopacity of a refractory metal generally follows the mass density of the metal, the greater the mass density the greater the radiopacity. However, the mechanical properties, i.e. elastic modulus, of the refractory metals do not follow the mass density. The mass density, elastic modulus and relative costs of suitable refractory metals and stainless steel (for comparison) are provided in the table below.
From the table above it becomes clear that rhenium and tungsten are very suitable metals, but their relatively high cost may preclude some applications. Tantalum has very good radiopacity but has relatively low strength and high costs. Niobium has marginally good radiopacity when compared to stainless steel but it is expensive and has lower mechanical properties than stainless steel. As a result niobium would have limited usage. Molybdenum has moderately high radiopacity, good mechanical properties and moderate cost and because of this combination of features will have more widespread usage than most of the other refractory metals.
Molybdenum containing strand material may be the metal alone or alloys thereof. Suitable alloying metals include tungsten, zirconium and halfnium. Preferably, tungsten may be included in amounts up to 30% (by wt), zirconium in amounts up to about 0.6% (by wt) and halfnium in amounts up to about 1% (by wt). Other alloying metal may also be utilized with molybedenum.
The radiopacity of the catheter is a function of both the level of radiopaque elements in the alloy, i.e. the refractory metal content, of the strands and the number and thickness of strands containing refractory metals. For adequate radiopacity at least 25% of the strands, preferably 75% of the strands of the reinforcing structure should be formed of the refractory metal containing material.
The elongated catheter shaft may have varied properties along the length. Typically, the elongated catheter shaft has increased flexibility in the distal direction by forming the catheter wall with polymeric materials having decreasing stiffness, i.e. distally decreasing durometers.
One embodiment of the catheter shaft having features of the invention includes a polymeric tube which forms the inner lining for the catheter shaft having multiple strands (e.g. 4 to 32 strands, typically 12, 16 or 24 strands) of suitable material in the form of wire or ribbon. Preferably, the strands are braided or wound about the inner tubular member. A sufficient number of the strands are formed of refractory metal containing material to provide a reinforcing structure having a desired radiopacity and providing the desire mechanical properties to the catheter. An outer polymer jacket may then be provided on the exterior of the reinforcing structure by suitable means such as heat shrinking, extruding or dip forming a polymeric layer onto the surface of the reinforcing structure. A removable mandrel may be provided within the inner lumen defined by the inner lining during the manufacturing process to shape the catheter into its desired configuration while it is being formed. The strands which make up the reinforcing structure may be suitable secured together to form the multistrand reinforcement into a stiffer structure. A plurality of the cross points, where the individual strands cross, may be secured together by brazing, soldering, welding, suitable mechanical connections and the like to form the stiffer structure.
The braided or wound multistrand reinforcing structure extends through most of the length of the elongated catheter shaft except for the distal tip which is usually provided with relatively flexible non-reinforced polymeric tubular member to provide non-traumatic characteristics to the distal tip.
Providing a plurality of strands formed of the refractory metal containing material within the reinforcement structure strengthens the structure and minimizes the support the polymeric material must add to the catheter shaft structure. This allows for much thinner polymer layers, resulting in thinner catheter walls and provides for more supportive and consistent catheter shapes. In addition the strands formed of refractory metal containing materials within the multistrand reinforcing structure of the catheter provide increased radiopacity over other strands previously used.